This invention relates to tank filler neck caps designed to withstand the application of excessive torque. More particularly, the present invention relates to filler neck caps having a ratchet wheel for providing a driving connection between a shell and a housing in such a way that the shell disengages from the housing under the application of excessive torque to the shell.
In recent years, caps configured to be screwed onto fuel tank filler necks have included a torque-control mechanism therein to prevent users from overtightening the cap on the filler neck. Each cap typically includes an O-ring gasket that establishes a fluid and vapor seal between the cap and the filler neck once the cap is mounted properly on the filler neck. Frequent overtightening of a filler neck fuel cap can crush or otherwise damage the O-ring gasket which provides the seal between the cap and the filler neck. The torque-control mechanism was developed to limit the amount of torque which could be applied by a user in the cap-advancing direction as the user rotates the cap on the filler neck to its fully seated filler neck-closing position thereon. Thus, a torque-control mechanism helps minimize wear and tear on the O-ring gasket and preserves the sealing capability of the gasket.
Typically, the torque-control mechanism operates to transmit torque from the outer shell of the cap to the filler neck-engaging closure member of the cap until the closure member is rotated to its fully seated position on the filler neck and the magnitude of the torque begins to exceed a predetermined level. A resilient finger having a pawl tooth at its outer end has been used to engage notches formed in the underside of the outer shell to provide a torque-override driving connection between the outer shell and the closure member as shown, for example, in U.S. Pat. No. 4,913,303 to Harris. See also U.S. Pat. Nos. 4,666,056; 4,726,488; and 4,795,053. Under the application of excess torque to the outer shell, the resilient fingers flex and disengage from the notches in the outer shell to allow the outer shell to rotate relative to the fully seated closure member.
It has been observed that the resilient fingers used in conventional torque-control mechanisms have some shortcomings which can lead to dysfunction of the torque-control mechanism. Typically, these resilient fingers are relatively long and are few in number. Thus, the loading on the pawl of each individual finger is relatively high, contributing to fatigue of the resilient fingers over time. In addition, the resilient fingers may suffer from continuous exposure to high temperature conditions of the type which would be encountered in, for example, a vehicle radiator. The resilient fingers are fashioned of polymeric materials which tend to wear and relax under high temperature conditions. Eventually the resilient fingers become so flexible that they are unable to maintain a driving connection between the ratchet projections and the pawls.
One object of the invention is to provide a filler neck cap having a torque-control mechanism that functions well in a high temperature environment such as in a vehicle cooling system filler neck.
Another object of the invention is to provide a filler neck cap having a torque-control mechanism that is able to withstand repeated application of excessive torque over a long period of time without impairing the driving mechanism in the cap which establishes a driving connection between the outer shell and the closure member during installation and removal of the filler neck cap.
Still another object of the present invention is to provide a torque-override cap having drive teeth designed to maintain sufficient rigidity under high temperature conditions to provide a torque-override function when the cap is rotated about an axis of rotation in a cap-advancing direction.
According to the present invention, a cap for use in closing a filler neck of a tank includes a housing provided with means for engaging the filler neck and shell means for providing a hand grip. The shell means includes a plurality of drive teeth.
The cap further includes a ratchet wheel disposed between the housing and the shell means and connected to the housing for rotation therewith. The ratchet wheel includes a plurality of driven teeth configured to engage the drive teeth. The engagement of the driven teeth and the drive teeth provides a torque-limited connection in the cap-advancing direction and a positive connection in the cap-removal direction.
In preferred embodiments of the present invention, the cap also includes spring means for yieldably biasing the driven teeth of the ratchet wheel into engagement with the drive teeth of the shell means to establish the torque-limited and positive connections. The spring means is illustratively a wavy washer that is positioned in an annular region in the housing to act between the housing and the ratchet wheel to urge the ratchet wheel toward the drive teeth formed on the underside of the shell means.
One feature of a preferred embodiment of the present invention is a ratchet wheel having a number of driven teeth substantially equivalent to the number of drive teeth in the shell means. Advantageously, by providing equivalent numbers of drive teeth and driven teeth, the loading caused by application of torque to the shell means is distributed evenly along the circumference of the ratchet wheel rather than being concentrated in a relatively limited number of resilient fingers. Thus, the fatigue on each individual tooth is minimized.
Another feature of a preferred embodiment of the present invention is a ratchet wheel having a plurality of driven teeth formed of a rigid material. Advantageously, the teeth will maintain rigidity under high temperature conditions so as to maintain a driving connection between the shell means and the housing. Such a ratchet wheel is well-suited for use in a torque-control mechanism to be used in a high temperature environment such as in the filler neck of a vehicle cooling system.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.